I have a question about vector (read description)

Question

https://code.sololearn.com/cr4M6UTF0pG5/?ref=app

1. what happens at line 15?(working)
2. why the destructor will be executed before line 16?

Answer 1

@AJbura @Xan I hoped that my previous comment will push you in a right direction. Unfortunately, not. So, here is direct answer on your question:
https://code.sololearn.com/c8qIYdrgN3qF/?ref=app

Answer 2

Xan but i don't understand why vector <A> v(5, 6);
create object. cause constructor is execute whenever the object is created.

Answer 3

now i got it thanks Nevfy

Answer 4

it's work like vector go for the class and (ctor) create elements came back (dtor). And when the program or main return 0; the all vector data obj was destroyed and for all detor is executed.

Answer 5

When you create a Vector of Class transmitting some parameters to the constructor, it works like that: one exemplar of Class is created and then Vector is filled by copying this exemplar, after that this exemplar is destroyed. It is like that even if you create a Vector of one element.
However, if you create a Vector of Class without transmitting any parameters to the constructor, this constructor will be called as many times as the number of elements in your Vector. Check this out here:
https://code.sololearn.com/cR3607a73eNF/?ref=app
And compare it with the previous case:
https://code.sololearn.com/c8qIYdrgN3qF/?ref=app

Answer 6

I added some debug code:
https://code.sololearn.com/cmo1Oelca9de/#cpp

The output was:

Constructor start: cnt = 0

Destructor start: cnt = 0

Destructor end: cnt = 1

In Main: cnt = 1

Destructor start: cnt = 1

Destructor end: cnt = 2

Destructor start: cnt = 2

Destructor end: cnt = 3

Destructor start: cnt = 3

Destructor end: cnt = 4

Destructor start: cnt = 4

Destructor end: cnt = 5

Destructor start: cnt = 5

Destructor end: cnt = 6

Answer 7

it's help me. try to change the value (5,6) with (1, 6).
the destructor execution depend on first element , but why don't know.

Answer 8

we have
vector <A> v(5, 1);

so, what is 5 & 1

Answer 9

In my understanding, that's how vector works. If you make the same counter for constructor, you will see that it is also called only once, however several elements were created.

Answer 10

Yes, I'm confused too.

I thought more debugging output would help you :-)

Answer 11

AJbura Great work ☺

Answer 12

5 is x-axis and y